Composite panels and methods of making them are well known. A composite panel generally includes a core member or plate, usually made of wood chips and similar particles that are consolidated into boards and the like. Other materials are basically applicable as well, including natural wood boards, synthetic resin slabs and the like.
A cover, protective laminate, or cover plate is glued onto the upper side of the core member. This is usually a high-pressure laminate (e.g. a phenolic laminate) as described in German Industrial Standard DIN 16 926 for HPL plate. Plates or sheets made of other materials, for example thermosetting and thermoplastic materials, veneers and metal are known, and the material selection will be dictated by the application at hand.
The cover glued onto the core member or sheet should be resistant to water and heat, which makes high-pressure multilayer plates particularly desirable. Frequently, the lower side, bottom or underside of the core member is also covered with a high-pressure laminate plate.
One of the difficulties associated with such composite panels is the proper protection, edging, and covering of the peripheral edges or rims. At one edge, i.e. that shorter side which corresponds generally to the panel width, or at opposing edges, protection and cover may be provided by extending the cover plate, which is glued onto the core member, in such a way that it may be brought over the respective edge for covering the edge, and then glueing it down. This is suggested in U.S. Pat. No. 3,849,235.
In this manner, the upper cover plate can form a continuum with the lower cover plate of such a composite plate or panel. When using special machines it is also possible to cover all four edges, or narrow sides, of a core member, by correspondingly surrounding these with the cover plate material. Such measures, however, are difficult to achieve in mass or serial production. Furthermore, even such four-way enclosing techniques leave gaps which will cause problems.
Accordingly, for reasons of production, economics and esthetics, the art generally suggests that only two narrow sides or edges of the core member are to be covered as briefly indicated in the foregoing. The remaining open edges are covered by separate protective covers. These additional covers or edge strips are variously known as glue-around-strips, endless-edges, and the like. They are made of the same material as the respective cover plate after cutting thereof. (See the brochure P 69 15982 of the firm Duropal-Werk Eberh. Wrede GmbH a Co. KG, Arnsberg, Germany with the title "Hochdruck-Qualite,uml/a/ ten" or "High Pressure Quality in The Production Program of Das Leistungsprogramm von DUROpal".)
The known composite panel described above is associated with the long-standing problem of certain production tolerances or clearances of the core member. For example, when using as a core member a piece of lumber with a thickness of 18 mm, one would attempt to achieve an accuracy of at least+/-0.5 mm, and at best+/-0.3 mm. In comparison with this, the respective production tolerances of the covers and the edge strips are negligible. At a thickness of 0.8 mm with negligible tolerance for the cover plate, the overall height or thickness is 19.6 mm +/-0.5 mm (preferably+/-0.3 mm).
The edge strip with its negligible tolerance is generally cut somewhat wider, or narrower, from the respective material, which is either the same as the cover plate, or made of another material, for example aluminum. This gives rise to gaps which present problems and difficulties, particularly moisture-related difficulties. In addition, it is quite common that the edge s strip can laterally shift during or after the glueing thereof to the rim or narrow side of a core member. The gaps would then undesirably increase in size, or sudden steps are created at the edge or narrow side of the core member.
It has previously attempted to avoid this problem by cutting the edge strip to a width which is adapted to the upper tolerance limit of the core member. After glueing the edge strip, the edges of the strip would be further adjusted to attain the correct size. As well, the respective edges were usually also rounded.
When considering overall production requirements, such a method is cumbersome and expensive. Also, it is generally not feasible to avoid damage to, or other effects of, the cover plate which may be caused by the tools that rework the edges of the edge strip. When using special decorative cover plates, this is particularly detrimental. For example, a special surface texture or grain texture is damaged at the edges, or is similarly affected. This applies even then when using an edge strip that is fully dyed or colored and in which, accordingly, no dark intermediate layers are discernable. In summary, the affected peripheral regions of such composite panels do not meet the high demands made by designers or builders.
The gaps for or due to glueing at the edge strips also present problems because they may allow entry of moisture, either by diffusion or by capillary action. Entry of moisture is a considerable problem when the core member is made of solid lumber, or is made of wood chips. At such gaps, the core member is protected against entry of moisture only by the glue itself, and even minute irregularities during glueing can lead to difficulties. This applies in the case of glueing any material. The customary materials have been, of course, well known for many years.